[uClinux-dev] 2.4.x questions

Bernhard Kuhn bkuhn at lineo.com
Thu Nov 15 09:07:17 EST 2001


Travis Griggs schrieb:

> 2) In the same menu, there is an option for the Kernel to execute from
> HIMEM. What is this?

This is an option originaly intended for Dragonball to
locate the kernel+romfs at 0x600000 (topmost 2MB of the
8MB RAM) instead of 0x10c00000 (2MB Flash).

The idea is to speed up downloading experimental kernels
during development: The uCsimm/uCdimm bootloader does
only support a slow serial connection - no tftp-download
via ethernet. So the kernel+romfs flashed is only
used as a bootloader for the experimental kernel.
There is also a user-space program called "himemloader"
that loads an image to 0x600000 and executes it from there.
In order to do so, the (flashed and experimental) kernel has
to be told to reduce the amount af available RAM by 2MB
(CONFIG_MEMORY_RESERVE, only available for uCsimm/uCdimm)

So to not confuse ppl, the entry in arch/m68nommu/config.in
should look like this:

if [ "$CONFIG_UCSIMM" = "y" -o "$CONFIG_UCDIMM" = "y" ]; then

choice 'Kernel executes from' \
        "RAM    CONFIG_RAMKERNEL \
         ROM    CONFIG_ROMKERNEL \
         HIMEM  CONFIG_HIMEMKERNEL" ROM

else

choice 'Kernel executes from' \
        "RAM    CONFIG_RAMKERNEL \
         ROM    CONFIG_ROMKERNEL" ROM

fi


> 3) Anothert menu is the MTD one. If I've got the M5272C3 board, are any
> of these things going to be useful to me? It seemed like this might give
> me run time control over the flash ram, but I'm kind of new to this
> flash stuff.

MTD is not a simple matter. I am just putting together some
documentation on how to create your own MTD mapping driver
(especialy for M5272C3), and how to create and flash a
cramfs-images. BTW.: i didn't had good luck with jffs:
the kernel crashes just after writing something to the
partition. This also happens on a standard PC. I know
we (Lineo) have i.e. a BSP for a PPC board where jffs is
working perfectly, but nobody could tell me what i am doing
wrong. Supposedly, everything should work fine ootb ...



-- 
Bernhard Kuhn, Software Engineer, Lineo Inc. (Where Open Meets Smart)
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